Efficacy of Essential Oils from Geranium (Pelargonium graveolens) and Citronella (Cymbopogon nardus) and Their Major Compounds Against Meloidogyne graminicola in Pots and Field Conditions

Pot and field experiments of Pelargonium graveolens (geranium), Cymbopogon nardus (citronella) oils and their major metabolites (citronellol and citronellal) were carried out for their nematicidal activity against Meloidogyne graminicola (root-knot nematode) at 500 and 1000ppm concentration using drenching and root dipping methods with direct seeded and transplanted rice. Results of the pot experiments showed the variable nematicidal activity of essential oils and pure compounds. Citronella oil (3.33 galls/seedling) and citronellal (3.33 galls/seedling) showed promising nematode controlling activity followed by geranium oil (3.67 galls/seedling) and citronellol (4.33 galls/seedling) at 1000 ppm on 30 days after inoculation (DAI) and were at par with carbofuran 3G (3.33 galls/seedling) and velum prime (3.33 galls/seedling), used as positive controls but found better than negative control (14.67 galls/seedling) in pot experiment. The plant growth of rice seedlings followed the pattern as citronella oil (35.0cm) > geranium oil (34.67cm)> citronellol (31.67cm) > citronellal (31.67cm) @ 1000 ppm at 30 DAI, compared to carbofuran (33.67cm) and velum prime (33.33cm). These results from pot experiment showed the promising activity of oil and compounds similar to positive controls. Citronella and geranium oils were further evaluated in a sick plot (1.0mx1.0m) at two concentrations (500 and 1000ppm) using drenching and seedling dip methods together with commercial nematicides. Results also showed that the plant growth (shoot length) of the rice seedlings in treatment with oil (@ 1000 ppm) were at par with carbofuran 3G and velum prime treatments but higher than negative control. The number of galls in citronella oil (0.6/seedling), carbofuran (0.6/seedling) were recorded less compared to velum prime (1.0/seedling) at 1000 ppm and negative control (3.8/seedling) under field conditions on 30day after showing (DAS). This study showed that the citronella and geranium oils could be an alternative to the commercial nematicides for controlling of M. graminicola up to 30 days after showing in direct seeded rice nursery.